P1233: TUMOR PREVENTION USING DNA DEMETHYLATING AGENTS ON VIRUS-DERIVED CARCINOGENESIS IN MICE.
Authors: Yuta Yamamoto, Tatsuro Watanabe, Hiroshi Ureshino, Kazuharu Kamachi, Yuki Kurahashi, Satoshi Yamashita, Naoko Hattori, Toshikazu Ushijima, Shinya Kimura
Journal: HemaSphere (2023)

Topic: 20. Lymphoma Biology & Translational Research Background: About 12-20% of human cancers are thought to be caused by viral infections. Human T-lymphotropic virus 1 (HTLV-1) is a cause of adult T-cell leukemia/lymphoma (ATL). ATL was the first recognized retrovirus-induced human malignancy and around 20 million people are infected with HTLV-1 worldwide. We have found that regional DNA hypermethylation accumulates in HTLV-1-infected T cells in ATL leukemogenesis and DNA demethylating agents inhibit ATL cell growth. Other types of carcinogenesis associated with oncovirus, including human papillomavirus-associated head and neck squamous cell carcinoma and Epstein-Barr virus-positive gastric cancer, also exhibit aberrant DNA hypermethylation status and susceptibility to DNA demethylating agents. Therefore, we hypothesized that carcinogenesis associated with oncovirus could be delayed through inhibiting DNA hypermethylation. Aims: This study aimed to examine the efficacy of a new DNA demethylating agent, OR-2100 which we developed as an orally bioavailable decitabine prodrug, on virus-derived carcinogenesis in a mouse model. Methods: AKR/NSlc (AKR) mice which spontaneously develop lymphocytic leukemia around 6-12 months of age, were from Japan SLC, Inc. AKR mice express in all tissues the retrovirus AKV, which is associated with spontaneous leukemia development in mice. Decitabine and a prodrug of decitabine, OR-2100 (OR21) were administered i.p. to AKR mice twice a week from 6 weeks old. A leukemic cell line derived from peripheral blood mononuclear cells of AKR mice (BW5147.G.1.4.OUA-R.1) was used for in vitro experiments. Results: OR-2100 (OR21) is a sylilated derivative of decitabine (DAC) and releases DAC sustainedly. The area under the curve value for total DAC after an intraperitoneal injection of OR21 was almost one-third of that observed when equimolar amounts of DAC were injected. Almost all AKR mice in the DAC (1 mg/kg and 2 mg/kg) and OR (6 mg/kg) groups died due to drug-induced hematological toxicity (Fig. A). All mice died of lymphocytic leukemia by 300 days of age in the vehicle group, whereas treatment with OR21 (2 mg/kg and 3 mg/kg) dramatically prolonged survival with lower hematological toxicity (Fig. A, B). Next, genome-wide DNA methylation profile and transcriptome of tumor cells isolated from the thymus of aged AKR mice were compared with those of control thymus isolated from young AKR mice. We found that gene expression of PAX5, a tumor suppressor gene in mouse mutagenesis models of acute lymphoblastic leukemia, was down-regulated with DNA hypermethylation in tumor cells(Fig. C). DNA hypermethylation in PAX5 was also observed in the leukemic cell line derived from AKR mice (BW5147.G.1.4.OUA-R.1). Treatment of BW5147.G.1.4.OUA-R.1 cells with DNA demethylating agents decreased DNA methylation and increased gene expression of PAX5 in a concentration-dependent manner (Fig. D, E). Protein expression of PAX5 was decreased at tumor onset in AKR mice and was even lower in the cell line (Fig. F), and it was increased by treatment with DNA demethylating agents in a concentration-dependent manner (Fig. G). Taken together, we believe PAX5 act as a tumor suppresser gene in spontaneous leukemogenesis in AKR mice. Summary/Conclusion: Aberrant DNA methylation was a possible cause of spontaneous leukemogenesis in AKR mice, a mouse model of virus-derived carcinogenesis. Furthermore, OR21 was safely used for long term treatment of AKR mice and prolonged survival. We believe OR21 has potential for use in the treatment of virus-associated cancers.Keywords: Hypomethylating agents, Lymphoma, Mouse model, Methylation